1. Field of the Invention
The present invention relates to a device of controlling a machine tool, to control a synchronized operation of a spindle axis and a feed axis. The present invention also relates to a method of controlling a machine tool, to control a synchronized operation of a spindle axis and a feed axis.
2. Description of the Related Art
In a machine tool capable of performing a tapping process by a synchronized operation of a spindle (or principal) axis and a feed axis, various kinds of configurations for improving processing accuracy and reducing cycle time have been proposed. For example, a thread forming apparatus that performs a tapping process by operating a feed axis to follow the rotation of a spindle axis has been known, in which a feed command value for the feed axis is computed based on the rotational speed and rotational acceleration of the spindle axis and a thread pitch, and the feed command value is corrected in accordance with the actual rotational position of the spindle axis, so as to improve tapping accuracy (see, e.g., Japanese Patent No. 2629729 (JP 2629729 B)). On the other hand, a method of acceleration and deceleration control of a spindle motor, executed by a numerical control unit that performs synchronization control of a spindle axis and a feed axis for a tapping process, has been known, in which the numerical control unit prepares an acceleration and deceleration command in conformity with the power characteristics of the spindle axis, and controls the spindle axis based on the acceleration and deceleration command to improve the response of the spindle axis, so as to reduce cycle time (see, e.g., Japanese Patent No. 3553741 (JP 3553741 B)).
Further, a controller of a machine tool, having a configuration for controlling a synchronized operation of a spindle axis and a feed axis, has been known, wherein a numerical control section sends a spindle-axis command to the spindle-axis control section, based on a tapping program, the spindle-axis command including a total rotation amount and a maximum rotation speed of the spindle axis during a period when the spindle axis operates from a process start position to a target thread depth, and a spindle-axis control section makes the spindle axis automatically perform an accelerated and decelerated rotation at maximum capacity in accordance with the spindle-axis command, so as to perform a tapping process (see, e.g., Japanese Unexamined Patent Publication No. 2016-078223 (JP 2016-078223 A)).